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(1). Field of the Invention
The present invention relates to a process which enables the treatment of organic matter contaminated drinking water. In particular, the present invention uses a combination of the addition of a carbon source to a fluidized bed bioreactor and ozonated organic matter to biodegrade the ozonated organic matter and carbon source and thus purify the water.
(2). Description of Related Art
The use of beds containing microorganisms in an aerobic biological environment which degrades pollutant organic matter in water is well known in the prior art. Further, the use of ozone to oxidize the organic matter for biodegradation is well known in the prior art. U.S. Pat. No. 5,851,399 to Leitzke describes such a process using a fixed bed reaction vessel. U.S. Pat. No. 3,779,909 to Wisfeld et al also describes a similar fixed bed process. Various other patents are as follows: U.S. Pat. No. 5,954,963 to Matheson; U.S. Pat. No. 5,942,118 to Besten; U.S. Pat. No. 5,885,826 to Worden et al; U.S. Pat. No. 5,711,887 to Gastman et al; U.S. Pat. No. 5,512,178 to Dempo; U.S. Pat. No. 5,505,856 to Campen et al; U.S. Pat. No. 5,466,374 to Bachhofer et al; U.S. Pat. No. 5,346,617 to Costello; U.S. Pat. No. 5,336,413 to van Staveren; U.S. Pat. No. 5,211,847 to Kanow; U.S. Pat. No. 4,693,827 to Mordorski U.S. Pat. No. 4,255,266 to Moreaud et al; U.S. Pat. No. 4,178,239 to Lowther; and U.S. Pat. No. 3,836,456 to Fries.
U.S. Pat. No. 4,693,827 Mordoski describes a fixed bed method for accelerating the start-up of biological nitrification systems for wastewater treatment and preventing reducing the effects of toxic and inhibitory materials or excursions of pH, temperature, or dissolved oxygen upon nitrifying organisms. A rapidly metabolized soluble or miscible organic material containing little or no nitrogen is added to the carbon-consuming step of the process. Heterotrophic organisms consume the added material together with soluble ammonia to generate additional organisms. The soluble ammonia concentration in the wastewater is reduced to a nontoxic, less toxic, or less inhibitory level. The goal is to increase the removal of ammonia nitrogen from wastewater by adding rapidly metabolized carbon source. The carbon source provides growth of heterotrophic microorganisms that consume ammonia nitrogen which is incorporated into cellular matter (the C:H:O:N ratio of bacterial cells is typically about 52:6:26:12). This reference describes the use of additional rapidly metabolized carbon source to increase biomass concentration; the use of chemical compounds such as carbon supplements (alcohols, organic acids, and the like) for the degradation; and that the carbon source is added to the water stream just prior to or directly to the stage which removes carbonaceous materials from water. The patented method pertains to the removal of ammonia nitrogen, but not to the removal of organic matter initially present in water.
U.S. Pat. No. 5,954,963 to Matheson describes a fixed bed process and apparatus for biologically treating water without using ozone. The inventive process preferably comprises the steps of: (a) adding a sulfur-containing oxygen scavenger to the water in an amount effective for at least reducing the amount of dissolved free oxygen in the water; (b) removing at least a portion of a substance from the water by exposing the water to microorganisms effective for biologically removing the substance therefrom; and (c) feeding a biostimulant to the microorganisms effective for increasing the rate at which step (b) occurs. The inventive apparatus preferably comprises a system for adding the sulfur-containing oxygen scavenger to the source water stream and a system for feeding the biostimulant to the microorganisms. The invention particularly relates to processes and apparatuses for the biological denitrification of water.
The patent describes the use of a biostimulant to the microorganisms to increase the rate at which a substance is removed from water; the use of low molecular weight organic compounds as carbon supplements for the purpose of invention (alcohols, organic acids, and the like); and the use of a carbon source added to the water stream at a point located at a very short distance upstream of the bioreactor.
The process of Matheson pertains to biological denitrification of water, and not the removal of organic matter present in water. The Matheson process is not capable of effectively removing organic matter (particularly humic substances, which are disinfection by-product precursors) from water. This is because most of the organic matter present in water cannot be effectively degraded by purely biological means. As a result, while microorganisms consume the biostimulant, little or no removal of organic matter present in water occurs. No ozonation is used first to convert nonbiodegradable organic materials into biodegradable organic matter and then xe2x80x9cstimulatedxe2x80x9d biodegradation is used to increase the rate at which this biodegradable organic matter is removed by microorganisms. In Matheson, the carbon source (an organic compound) may be added.
U.S. Pat. No. 5,851,399 to Leitzke describes a fixed bed process which serves for treating water polluted with pollutants which can only be degraded with difficulty by purely biological means. The water is circulated through a reactor vessel arrangement in which it is treated with ozone which causes a preliminary oxidation of the pollutants. The water passes into a vessel arrangement containing an aerobic biological treatment which, owing to the preliminary oxidation of the pollutants, is able to degrade these further. It can be inferred from the description, that water alternately passes through ozonation and biodegradation stages so that ozone is used to break down nonbiodegradable materials and convert them into biodegradable materials, which are removed at the biodegradation stage.
Leitzke describes the use of recirculation through ozonation and biodegradation stages. The Leitzke process was not effective for either the removal of natural organic matter present in water or producing biologically stable water. This is because ozonation of natural organic matter produces a significant amount of slowly biodegradable organic matter, which is difficult to remove by biodegradation. There is no disclosure of a rapidly metabolized carbon source which increases the rate at which these biodegradable materials are biodegraded, thus, significantly enhancing the effect of recirculation on process efficiency.
U.S. Pat. No. 5,466,374 to Bachhofer et al and Locher describes a fixed bed process for purifying polluted water containing organic nutrients for microorganisms, the process including (a) mixing the organically polluted water intensively with ozone in an ozone treatment unit; (b) adding to the water of step (a) at least one compound containing sulfur, which at least one compound containing sulfur is bioavailable for assimilation by at least aerobic microorganisms; and (c) passing water of step (b) through a filter composed of a plurality of layers. The process may optionally include treating water after step (c) with ozone in an ozone water treatment unit in order to oxidize residual bioavailable sulfur. The compound containing sulfur is preferably added in an amount which is effective to at least eliminate sulfur deficiency of the aerobic microorganisms and promote growth of a biofilm in the filter thereby contributing to biological mineralization of the organic nutrients. The goal is to increase the bioavailability of organic pollutants by means of ozone and to increase the rate of biodegradation by adding sulfur containing compounds that promotes growth of biomass.
Bachhofer et al describe the use of ozone to convert nonbiodegradable materials into biodegradable organic matter; the use of biodegradation to remove biodegradable organic matter; and the addition of biostimulants to increase biodegradation rate by promoting growth of biomass.
The Bachhofer et al process implies that the growth of biomass is limited by the deficiency of sulfur in water. Therefore, adding a sulfur compound to water is a key element of this invention. They do not suggest that a source of carbon is a limiting factor.
U.S. Pat. No. 4,178,239 to Lowther describes a fixed bed process for intermediate treatment of aqueous sewage containing biodegradable materials and non-biodegradable materials. The sewage is contacted with an ozone-containing gas to pretreat the sewage by converting a substantial amount of the non-biodegradable material, followed by a conventional secondary treatment with an O2-containing gas such as air in the presence of aerobic or facultative anaerobic microorganisms. The process of combined ozonation and biodegradation is widely used in water treatment practice. Ozone is used to convert nonbiodegradable organic mater into biodegradable organic materials, which are degraded through the action of microorganisms. There is no use of a carbon source stimulant.
U.S. Pat. No. 5,211,847 to Kanow describes a denitrification method. U.S. Pat. No. 4,693,827 to Mordoski describes a similar process. U.S. Pat. No. 5,336,413 to van Staveren describes a fixed or fluidized bed process and apparatus for the purification of water, oxygen/ozone-gas mixture is introduced under high pressure in the water to be purified, and thus obtained oxygen/ozone-gas mixture enriched water is passed to a purification stage which comprises at least one reactor. Insufficiently degraded contaminants are retained by a membrane filter unit and recycled to the purification stage. Thus contaminants, such as hydrocarbon compounds and the like, are recirculated until they are converted to carbon dioxide and water. This reference is similar to Leitzke, except for membrane separation. There is no carbon source.
Fluidized beds are well known in the prior art. They are not used widely in the treatment of drinking water to remove pollutants. Most prior art reactors are fixed beds. The problem is that such beds tend to produce irregular treatment along the length of the fixed bed and are subject to clogging. There is a need for improvement.
The presence of naturally occurring organic matter (NOM) in drinking water is problematic due to the formation of trihalomethanes (THMs) and other halogenated compounds during disinfection with chlorine. Many of these disinfection by-products (DBPs) of chlorination of NOM are either carcinogenic or potentially carcinogenic, and, as such, their presence in drinking water is being increasingly regulated by U.S. Environmental Protection Agency. As a result, cost-effective treatment systems which are capable of reducing the formation of DBPs must be developed.
Most conventional ozonation/biodegradation treatment processes (e.g. the Mxc3xclheim process, the Metropolitan Water District process, the Andover process, and the EBMUD process) are sequential processes in which ozone is applied prior to biofiltration. This means that a portion of ozone is consumed by some organic compounds (original organics or ozonation by-products) that could have otherwise been degraded biologically.
To prevent biofilters from clogging, most conventional ozonation/biodegradation treatment processes require additional pretreatment, such as coagulation/flocculation/sedimentation (e.g., the Metropolitan Water District process, the Andover process, and the EBMUD process) or powdered-activated-carbon treatment (e.g., the Mxc3xclheim process), which are used either before ozonation (e.g., the Mxc3xclheim process, the Metropolitan Water District process, and the EBMUD process) or between ozonation and biofiltration steps (e.g., the Andover process). This prevents clogging of the bed containing the microorganisms.
Prior art systems are poorly controlled and must be custom-designed for each specific application. Standard-size units that have small footprint and in many cases can be skid-mounted would be desirable. The process performance of the unit could be optimized for different sources of water supplies. The system should also be capable of meeting future effluent standards through process parameter optimization without plant expansion or process modification. The system is preferably monitored and controlled from remote locations using advanced telemetry, thus reducing operating and maintenance costs.
The present invention relates to a process for the treatment of water to reduce amounts of pollutants in the water which comprises:
(a) directing the water containing the pollutants, which pollutants are ozonated, through a microbiologically active fluidized bed of particles in a vessel with an inlet and an outlet for the water so that the bed is fluidized by the water and the pollutants are degraded by microorganisms in the bed;
(b) providing a carbon source for the microorganisms in the fluidized bed in the vessel as the water is moved through the fluidized bed in the vessel, wherein the carbon source and pollutants are co-metabolized by the microorganisms and a effluent is removed from the outlet from the vessel; and
(c) filtering the effluent from the vessel, wherein the water with the reduced amounts of the pollutants is produced.
The term xe2x80x9cwaterxe2x80x9d as used herein means aqueous liquids which can contain small portions of other liquids which do not interfere with the processing. Usually the amounts are between about 1 mg and 50 mg per liter.
The term xe2x80x9cpollutantxe2x80x9d or xe2x80x9cpollutantsxe2x80x9d means carbon compounds and nitrogen compounds or combinations thereof.
The term xe2x80x9cmicrobiologically activexe2x80x9d means containing microorganisms, usually bacteria which function in an aerobic environment. Such bacteria are for instance Pseudomonas, Bacillus, and other oil bacteria. Typically the microorganisms are produced naturally in the bed, but can be added as supplied from commercial sources.
The term xe2x80x9cbedxe2x80x9d means a solid surface of particles to which the microorganisms adhere. Such beds preferably are particles of an inorganic process, water insoluble material preferably having an average particle size of about 8 and 30 mesh (standard US). Sand or activated carbon can be used.
The term xe2x80x9cfluidizedxe2x80x9d means that the particles in the bed are suspended by the motion of the water through the bed. The temperatures of the water in the bed are between about 1 and 45xc2x0 C.
The abbreviation xe2x80x9cDBPxe2x80x9d means disinfection by-products from ozonation and chemical water treatment.
The abbreviation NOM means naturally occurring organic matter in water.
The abbreviation xe2x80x9cTHMxe2x80x9d means trihalomethanes (chloroform, bromodichloromethane, dibromochloromethane, and bromoform) produced from disinfection of water with chlorine.
The xe2x80x9ccarbon sourcexe2x80x9d is preferably water soluble and is preferably an easily biodegradable compound such as lower alkyl alkanols, acids and salts containing 1 to 6 carbon atoms.
The inventive process preferably comprises the steps of: (a) treating water to break down organic matter with ozone in the amount effective for converting all or some nonbiodegradable organic matter present in water into biodegradable materials; (b) treating water from step (a) in a biologically active fluidized bed system in order to remove biodegradable organic matter; and (c) adding a biostimulant at step (b) in order to increase biodegradation efficiency of step (b). The process may optionally include recycling a portion of the water from step (b) back to step (a) in order to further convert remaining nonbiodegradable organic matter into biodegradable materials. The inventive process may alternately comprise the steps of: (a) treating water in a biological fluidized bed treatment system in order to remove some organic matter present in water; (b) adding a biostimulant at step (a) in order to increase biodegradation efficiency of step (b); (c) treating the water after step (a) with ozone in order to convert nonbiodegradable organic matter into biodegradable material; and (d) biologically treating the water after step (c) in order to remove biodegradable organic matter produced after step (c). The alternative process may optionally include recycling a portion of the water after step (c) back to step (a) in order to increase the efficiency of the removal of biodegradable organic matter produced after step (c).
It is therefore an object of the present invention to provide a process for the treatment of water to remove pollutants. Further, it is an object of the present invention to provide a process which can be easily scaled to any volume of water purification, particularly drinking water. Further still, it is an object of the present invention to provide a process which is relatively economical to perform with commercially available equipment components. These and other objects will become increasingly apparent by reference to the following description and the drawings.